21972161 has 4 divisors (see below), whose sum is σ = 22117824. Its totient is φ = 21826500.

The previous prime is 21972127. The next prime is 21972173. The reversal of 21972161 is 16127912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21972161 - 2²² = 17777857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21972101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 72605 + ... + 72906.

It is an arithmetic number, because the mean of its divisors is an integer number (5529456).

Almost surely, 2^21972161 is an apocalyptic number.

It is an amenable number.

21972161 is a deficient number, since it is larger than the sum of its proper divisors (145663).

21972161 is a wasteful number, since it uses less digits than its factorization.

21972161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 145662.

The product of its digits is 1512, while the sum is 29.

The square root of 21972161 is about 4687.4471730357. The cubic root of 21972161 is about 280.0856923091.

The spelling of 21972161 in words is "twenty-one million, nine hundred seventy-two thousand, one hundred sixty-one".